Police are to carry out a review of evidence Nigella Lawson gave during the fraud trial of Francesca and Elisabetta Grillo, her former personal assistants

Nigella Lawson is facing a police investigation into her admission that she used drugs after a dramatic about-turn by Scotland Yard on Saturday night.

Police are to carry out a review of evidence she gave during the fraud trial of Francesca and Elisabetta Grillo, her former personal assistants.

In the witness box, she admitted taking cocaine several times, most recently in 2010, and smoking cannabis.

However, evidence was also given by the two women claiming she had repeatedly used the Class A drug.

When they were acquitted on Friday, Scotland Yard said it would not look at her admissions or the women’s claims. She would only be investigated if new evidence emerged.

But on Saturday night Commander Stephen Watson, of the Metropolitan Police, told The Telegraph that officers would examine the “implications” of what she had said under oath and seek advice on what to do next from the Crown Prosecution Service.

Police will consider whether to bring drug possession charges and could also interview her to attempt to identify her suppliers. Social services could also intervene either at the request of police or on their own initiative after claims that she used drugs in front of her children.

The developments came amid mounting anger from Miss Lawson and her supporters over what they see as a determined campaign to smear her and damage her career after the collapse of her marriage to Charles Saatchi, the art dealer.

The Telegraph has established fresh details of his role in the campaign, including how Mr Saatchi and the Grillo sisters used the same public relations representative.

In spite of the Grillo sisters being prosecuted for defrauding Mr Saatchi he is understood to have used Richard Hillgrove to plant stories about his ex-wife.

The adviser was also being used by the Grillos.

Friends said on Saturday night that Miss Lawson was furious about how allegations of her drug use had emerged. However, Miss Lawson’s supporters also made clear that she was pressing ahead with her work.

Mr Saatchi was understood last night to have left the country for a holiday in the Caribbean.

Miss Lawson’s spokesman disclosed that all her nine cookery books would be republished over the coming months with new cover designs.

A new television series called The Taste — in which she stars as a cooking competition judge — is to be shown for the first time in a prime-time slot on Channel 4 next month.

The disclosure is an apparent sign of the cook’s confidence that her career is unharmed by the court case.

However, she faces a new investigation which could be protracted. Mr Watson, one of Scotland Yard’s most senior officers, said officers would look at all aspects of what was said during the trial.

“We will use specialist resources from within the Metropolitan Police Service to examine all the evidence which emerged as part of a review into this matter,” he said. “At some point once that review is included, presumably in conjunction with the Crown Prosecution Service, we will determine a way forward.

“Part and parcel of that review we will undertake will be to look at all aspects of the testimony that was given in the trial, which is now public knowledge, and will reveal itself in the transcripts of the trial. There are implications in terms of what has been said during the course of that trial and all those implications will be taken into account in determining an appropriate way forward.”

On Friday, Scotland Yard issued a statement that said: “At this stage the Metropolitan Police will not be investigating these allegations."

But on Saturday Mr Watson said: “Frankly, I don’t think the full colour of the Metropolitan Police Service’s position was conveyed in that statement."

Scotland Yard’s new review is likely to focus on evidence Miss Lawson gave at Isleworth Crown Court on Dec 4.

The cook disclosed that she took the Class A drug on six occasions with John Diamond, her first husband, when he found out that he had terminal cancer.

“It gave him some escape," she told the court. “There was another time I took cocaine. In July 2010 I was having a very, very difficult time. I felt subjected to intimate terrorism by Mr Saatchi."

She added: “The idea that I am a drug addict or habitual user of cocaine is absolutely ridiculous."

Miss Lawson also admitted taking cannabis in the last year of her marriage to the multi-millionaire art gallery owner. "I have to be honest, I have smoked the odd joint," she said.

"I found it made an intolerable situation tolerable. It’s a false friend. I found the answer was in changing the situation and trying to create a tolerable situation for me and my family. Since freeing myself from a brilliant but brutal man, I’m now totally cannabis, cocaine and drug free."

She claimed in her evidence that Mr Saatchi had "told everyone" he was taking cocaine out of her nose after he was photographed holding her neck at Scott’s restaurant in central London. She said the incident was provoked by another, unrelated comment.

Elisabetta Grillo gave evidence to the trial on Dec 14 in which she claimed Miss Lawson "lets the children smoke weed".

Potential areas for the police to pursue include not just whether Miss Lawson should be charged, but whether she can identify the suppliers of the cocaine. They may also question Victoria Coren, who wrote in a national newspaper that she had taken cocaine with Mr Diamond before his death in 2001.

However, legal experts and police officers said pursuing a case against Miss Lawson presented several difficulties.

Prof David Nutt, the former government adviser on drugs laws, said: "The law in this country is based on possession of drugs, not on their use. The police would not be able to prove it."

Sally O’Neill QC, a criminal barrister from Furnival Chambers, said: "If someone does incriminate themselves giving evidence as a witness it would be highly unusual for them to be prosecuted."

One former senior police officer, who declined to be named, said: "Clearly she was getting her drugs from someone and that, surely, must be a matter of public interest.

"If I had been in charge of this fraud case in which Miss Lawson was a witness, I would have wanted to know the full facts about her drug use.

"There are also child protection issues about drugs and minors. Are the police going to ignore potential child protection issues in relation to a family just because they are rich, in a way they would not do if this family lived on a normal street in a normal town?"